A variety of systems are used in borehole geophysical exploration and production operations to determine chemical and physical parameters of materials in the borehole environs. The borehole environs include materials, such as fluids or formations, in the vicinity of a borehole as well as materials, such as fluids, within the borehole. The various systems include, but are not limited to, formation testers and borehole fluid analysis systems conveyed within the borehole. In all of these systems, it is preferred to make all measurements in real-time and within instrumentation in the borehole. However, methods that collect data and fluids for later retrieval and processing are not precluded.
Formation tester systems are used in the oil and gas industry primarily to measure pressure and other reservoir parameters of a formation penetrated by a borehole, and to collect and analyze fluids from the borehole environs to determine major constituents within the fluid. Formation testing systems are also used to determine a variety of properties of formation or reservoir in the vicinity of the borehole. These formation or reservoir properties, combined with in situ or uphole analyses of physical and chemical properties of the formation fluid, can be used to predict and evaluate production prospects of reservoirs penetrated by the borehole. By definition, formation fluid refers to any and all fluid including any mixture of fluids.
Regarding formation fluid sampling, it is of prime importance that fluid collected for analysis represents virgin formation fluid with little contamination from fluids used in the borehole drilling operation. Various techniques have been used to minimize sample contamination including the monitoring of fluid pumped through a borehole instrument or borehole “tool” of the formation tester system until one and/or more fluid properties, such as resistivity, cease to change as a function of time. Other techniques use multiple fluid input ports combined with borehole isolation elements such as packers and pad probes to minimize fluid contamination. Flowing fluid through the tool is analyzed until it has been determined that borehole fluid contamination has been minimized, at which time the fluid can be retained within the tool and typically returned to the surface of the earth for more detailed chemical and physical analyses. Regarding in situ analyses of formation fluid, it is of prime importance that fluid collected for analysis represents virgin formation fluid with little contamination from fluids used in the borehole drilling operation.
Fluid analyses typically include, but are not limited to, the determination of oil, water and gas constituents of the fluid. Technically, it is desirable to obtain multiple fluid analyses or samples as a function of depth within the borehole. Operationally, it is desirable to obtain these multiple analyses or samples during a single trip of the tool within the well borehole.
Formation tester tools can be conveyed along the borehole by variety of means including, but not limited too, a single or multi-conductor wireline, a “slick” line, a drill string, a permanent completion string, or a string of coiled tubing. Formation tester tools may be designed for wireline usage or as part of a drill string. Tool response data and information as well as tool operational data can be transferred to and from the surface of the earth using wireline, coiled tubing and drill string telemetry systems. Alternately, tool response data and information can be stored in memory within the tool for subsequent retrieval at the surface of the earth.
Prior art formation tester tools typically comprise one dedicated fluid flow line cooperating with a dedicated pump to draw fluid into the formation tester tool for analysis, sampling, and optionally for subsequent exhausting the fluid into the borehole. As an example, a sampling pad is pressed against the wall of the borehole. A probe port or “snorkel” is extended from the center of the pad and through any mudcake to make contact with formation material. Fluid is drawn into the formation tester tool via a dedicated flow line cooperating with the snorkel. In order to isolate this fluid flow into the probe from fluid flow from the borehole or from the contaminated zone, fluid can be drawn into a guard ring surrounding the snorkel. The guard fluid is transported within the tester tool via a dedicated flow line and a dedicated pump. A more detailed description of the probe and guard ring methodology is presented in U.S. Pat. No. 6,301,959 B1, which is here entered into this disclosure by reference. This reference also discloses a dedicated flow line through which the snorkel fluid flows, and a dedicated flow line through which guard fluid flows. Fluid is sampled for subsequent retrieval at the surface of the earth, or alternately exhausted to the borehole via the dedicated flow lines and pump systems.